In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged, and then exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is useful for light lens copying from an original or printing electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways.
Developing material commonly used in systems for developing latent images on the charge retentive surface typically comprises a mixture of toner and a "carrier" of larger granular beads of a ferrous material. If the developing system is a magnetic brush assembly, magnetizable carrier beads also provide mechanical control for the formation of magnetic brush bristles so that toner can readily be brought into contact with the charge retentive surface. Toner is attracted to the latent image from the carrier beads to form the toner image. In this type of copier, some carrier beads inevitably adhere to the charge retentive surface after the image is developed. Some of these adhering carrier beads may prevent perfect contact between the substrate and toner image during the transfer step. It is thus essential for optimum operation that carrier beads remaining on the charge retentive surface be removed therefrom. Failure to remove carrier beads from the charge retentive surface results in a characteristic copy quality defect displaying a white area which may have a black dot in the center. The hard carrier beads also have a tendency to abrade and damage the charge retentive surface if not removed prior to reaching the cleaning zone.
Carrier bead removal devices are known, such as, for example, those described in U.S. Pat. Nos. 3,894,513 to Stanley et al. and 3,834,804 to Bhagat et al., which use a stationary magnet within a rotating cylindrical shell to remove the ferrous carrier beads from the photoreceptor for deposit in a sump or for return to the developer housing.
U.S. Pat. No. 4,829,338 to Whittaker et al. describes an apparatus for magnetically picking excess carrier beads off a photoreceptor, using a shunted stationary magnet disposed within a rotating sleeve which contacts the photoreceptor near the exit of the developer housing. The magnet and the rotating sleeve extend across the photoreceptor belt 10, generally transverse to the direction of movement of the photoreceptor belt 10. This "bead removal device," or BRD, is common on many electrophotographic printers currently available, and is also used in conjunction with the present invention, to be described below.
When using a BRD as described above, or any other device for removing carrier beads which are adhering to the photoreceptor, a concern is that a certain number of carrier beads will not be removed, particularly those which adhere in areas near the edges of the photoreceptor. These carrier beads are likely to be outside the effective magnetic range of a BRD. Also, because the beads are near the edges of the photoreceptor, the beads are likely to migrate from the developer housing into the rest of the machine, very probably interfering with the operation of the machine.
It is an object of the present invention to provide a seal disposed at the edges of a moving photoreceptor to substantially reduce migration of carrier beads out of the developer housing.
It is another object to provide such a seal which is satisfactorily efficient, but which will not damage the photoreceptor.
It is another object to provide such a seal which may be manufactured from inexpensive materials.
Other objects will appear hereinafter.